有机薄膜晶体管及其集成电路

首先介绍了有机薄膜晶体管的基本结构、工作原理以及近期的研究进展。其次阐述了有机集成电路的重要组成部分——有机双极型晶体管的构建、工作机制和相关的发展状况。最后就有机集成电路的构建、加工以及未来的发展前景作了相关的阐述。     

Pentacene-Based Planar- and Vertical-Type Organic Thin-Film Transistor

Pentacene-based planar- and vertical-type organic thin-film transistors (OTFTs) are investigated in this paper. High operation voltages are observed for the planar-type OTFTs with top source/drain electrodes, which results from the limitations of channel length and low material mobility. With a reduced channel length, a LiF hole-injection enhancement layer, and a thin metal gate, the vertical-type pentacene OTFTs exhibit a low-voltage operation of less than 5 V and a compatible on/off ratio of larger than 10². The smaller current gain observed from the device under current modulation is attributed to the increase of base recombination current under the common-emitter mode.     

石墨烯电极有机薄膜晶体管研究

利用化学气相沉积法生长的高性能的层状石墨烯,通过转移和图案化后用作电极,制备了底接触的并五苯有机薄膜晶体管(OTFTs)。原子力显微镜观察发现,石墨烯电极的厚度比一般的金电极薄的多,所以石墨烯电极厚度对并五苯晶粒的生长影响不大。电学性能研究得到器件的输出和转移曲线、开关电流比、阈值电压、场效应迁移率。转移曲线的关态电流约为10-9 A,电流的开关比超过103。基于底接触的并五苯OTFTs的最大场效应迁移率约2×10-2 cm2.V-1.s-1。     

Structural Analysis on Organic Thin-Film Transistor With Device Simulation

A 2-D device simulation for organic thin-film transistors (OTFTs) was carried out to reveal the characteristic difference between staggered and planar structures. Assuming the OTFT with Schottky barrier contact, the staggered-structure TFT has more current flow, bigger field-effect mobility, and lower contact resistance than the planar structure. The simulation results indicate that the source electrode of the staggered structure has better ability to supply the current than that of the planar structure.     

Innovative Voltage Driving Pixel Circuit Using Organic Thin-Film Transistor for AMOLEDs

In this work, we propose a novel active-matrix organic light-emitting diode displays (AMOLED) pixel circuit based on organic thin-film transistor (OTFT) architecture, which consisted of four switches, one driving transistor, and a capacitor. The pentacene-based OTFT device possesses a field-effect mobility of 0.1 ${hbox{cm}}^{2} /{hbox{V}}cdot{hbox{s}}$, a threshold voltage of $-{hbox{1.5}}~{hbox{V}}$ , subthreshold slope of 1.8 V/decade and an on/off current ratio ${hbox{10}} ^{6}$. The resultant voltage-driving pixel circuit, named “Complementary Voltage-Induced Coupling Driving” (CVICD), is different from the current-driving scheme and can appropriately operate at low gray level for the low-mobility OTFT circuitry. The current non-uniformity less than 2.9% is achieved for data voltage ranging from 1 to 17 V by SPICE simulation work. In addition, the new external driving method can effectively reduce the complexity of OLED pixel circuitry.      

A Large Bandgap Organic Salt Dopant for Sn-Based Perovskite Thin-Film Transistor

Metal halide perovskite optoelectronic devices have made significant progress over the past few years, but precise control of charge carrier density through doping is essential for optimizing these devices. In this study, the potential of using an organic salt, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, as a dopant for Sn-based perovskite devices, is explored. Under optimized conditions, the thin film transistors based on the doped 2D/3D perovskite PEAFASnI₃ demonstrate remarkable improvement in hole mobility, reaching 7.45 cm²V⁻¹s⁻¹ with a low subthreshold swing and the smallest sweep hysteresis (ΔV_hysteresis = 2.27 V) and exceptional bias stability with the lowest contact resistance (2.2 kΩ cm). The bulky chemical structure of the dopant prevents it from penetrating the perovskite lattice and also surface passivation against Sn oxidation due to its hydrophobic nature surface. This improvement is attributed to the bifunctional effect of the dopant, which simultaneously passivates defects and improves crystal orientation. These findings provide new insights into potential molecular dopants that can be used in metal halide perovskite devices.     

A Novel Agglomerated-Silicon Thin-Film Transistor

This letter discusses the fabrication and electrical characteristics of a novel thin-film transistor (TFT) architecture based on intentionally agglomerated silicon for the active (island) region. Although the agglomeration of irradiated semiconductor is undesirable during the laser crystallization of polycrystalline-silicon TFTs, it is shown that precisely controlled wirelike structures can be obtained for certain conditions. Their width and pitch are maintained over very long distances, and their crystal structure is almost single crystal. Fabricated n- and p-channel TFT characteristics with maximum effective mobility values of 360 and 70 cm²/V ·s, respectively, are presented, with on/off current ratios exceeding ten decades.     

高性能有机薄膜晶体管(OTFT)制备及其导电机制

详细介绍了在SiO2和高kHfO2介质层上制备并五苯薄膜晶体管方面的研究,特别是利用原子力显微技术(AFM)和静电力显微技术(EFM)研究了并五苯分子初始生长模式,揭示了衬底形貌、表面化学性能(包括化学清洗和聚合物层修饰)对有机半导体成膜结构和薄膜场效应晶体管性能之间的关联,包括晶体管迁移率、开关比和阈值电压等;针对并五苯初始生长成核模式的差异,分析了不同岛(畴)间畴边界对载流子在有机薄膜内输运的影响,有助于理解有机半导体薄膜导电机理。通过优化和控制介电层和有机半导体薄膜层的界面化学性质,在SiO2介质层上成功制备出迁移率为1.0cm2/V.s、开关电流比达到106的OTFT器件;在高kHfO2介质层上获得的OTFT器件的工作电压在-5V以下,开关电流比达到105,载流子迁移率为0.6cm2/V.s;器件性能指标已经达到目前国际上文献报道的最好水平。     

A Testing Method on Poly-Si Thin-Film Transistor Array for Active-Matrix Organic Emitting Display

A novel method is introduced using to evaluate the quality of thin-film transistor (TFT) array for driving active-matrix display (OLED). By the means of this method, the operation states of the TFT or the defects of TFT can be judged. It is a current testing method with the advantages of fast response, excellent precision, no effect to aperture and no damage to the display array.     

Ultrathin Si Thin-Film Transistor on Glass

We have studied the fabrication of ultrathin single-crystalline-silicon thin-film transistors (TFTs) on glass. The single-crystalline Si layer was transferred to glass by hydrogen implantation and anodic bonding. The thickness of the silicon-on-glass (SiOG) was controlled down to 10 nm by dry etching. The p-channel SiOG TFTs with 10-nm-thick Si exhibited the field-effect mobility of 134.9 $hbox{cm}^{2}/hbox{V}cdot hbox{s}$, threshold voltage of $-$1.5 V, and gate voltage swing of 0.13 V/dec. The TFTs were found to be stable against gate bias stress of $+$30 or $-$30 V.      

A Conductivity Modulated Polysilicon Thin-Film Transistor

This paper reports a novel high voltage Conductivity Modulated Thin-Film Transistor (CMTFT) fabricated using polycrystalline silicon. The transistor uses the idea of conductivity modulation in the offset region to obtain a significant reduction in on-state resistance. Experimental on-state and off-state current-voltage characteristics of the CMTFT have been compared with those of the conventional offset drain device. Results show that the CMTFT has six times to more than three orders of magnitude higher on-state current handling capability for operating at drain voltages ranging from 15 V to 5 V while still maintaining low leakage current and providing even faster switching speed. The CMTFT devices can be fabricated using a low temperature process (620°C) which is highly desirable for large area electronic applications     

Fast PEALD ZnO Thin-Film Transistor Circuits

We report stable high-mobility ZnO thin-film transistors (TFTs) and fast circuits fabricated using a novel weak reactant plasma-enhanced atomic layer deposition (PEALD) process. This PEALD process is a highly scalable manufacturable process and is a faster and simpler alternative to conventional atomic layer deposition. Using PEALD, we have deposited highly crystalline (002) textured ZnO thin films at a low temperature (200 $^{circ}hbox{C}$). Using PEALD ZnO films, we have fabricated high-mobility TFTs (20–30 $hbox{cm}^{2}/hbox{V} cdot hbox{s}$ ), which have $≪$100-mV threshold voltage shifts after bias stress at 80 $^{circ}hbox{C}$ for 20 000 s. Using these high-performance TFTs, we have also fabricated simple 15-stage ring oscillator circuits with a propagation delay of 22 ns/stage for a supply voltage of 16 V, which, to the best of our knowledge, are the fastest ZnO TFT circuits reported to date.      

柔性晶体管阵列

现在市场上出现了柔性晶体管阵列并且前景诱人，但是在柔性阵列技术进入主流市场之前还要克服不少困难。     

Arbitrary Density of States in an Organic Thin-Film Field-Effect Transistor Model and Application to Pentacene Devices

We present a modular numerical model for organic thin-film field-effect transistors (OTFTs) that allows for an arbitrary density of states to be independently defined for the semiconductor bulk and the semiconductor surface next to the gate insulator. We can derive the surface charge density dependence on the interface field as well as the space-charge-limited current characteristics. Together with a model of the contacts, we arrive at a physical model that is applied to a series of OTFTs in staggered inverted (top contact) geometry with various gate insulator treatments     

Reliability of Active-Matrix Organic Light-Emitting-Diode Arrays With Amorphous Silicon Thin-Film Transistor Backplanes on Clear Plastic

We have fabricated active-matrix organic light emitting diode (AMOLED) test arrays on an optically clear high-temperature flexible plastic substrate at process temperatures as high as 285 degC using amorphous silicon thin-film transistors (a-Si TFTs). The substrate transparency allows for the operation of AMOLED pixels as bottom-emission devices, and the improved stability of the a-Si TFTs processed at higher temperatures significantly improves the reliability of the light emission over time.     

Small-Subthreshold-Swing and Low-Voltage Flexible Organic Thin-Film Transistors Which Use HfLaO as the Gate Dielectric

Pentacene organic thin-film transistors (OTFTs) with a high-$kappa$ HfLaO dielectric were integrated onto flexible polyimide substrates. The pentacene OTFTs exhibited good performance, such as a low subthreshold swing of 0.13 V/decade and a threshold voltage of $-$1.25 V. The field-effect mobility was 0.13 $hbox{cm}^{2}/hbox{V}cdothbox{s}$ at an operating voltage as low as only 2.5 V. These characteristics are attractive for high-switching-speed and low-power applications.      

High Performance Flexible Nonvolatile Memory Based on Vertical Organic Thin Film Transistor

Flexible floating‐gate organic transistor memory (FGOTM) is a potential candidate for emerging memory technologies. Unfortunately, conventional planar FGOTM suffers from weak driving ability and insufficient mechanical flexibility, which limits its commercial application. In this work, a novel flexible vertical FGOTM (VFGOTM) is reported. Benefitting from new vertical architecture, VFGOTM provides ultrashort channel length to afford an extremely high current density. Meanwhile, VFGOTM devices exhibit excellent memory performance and outstanding retention property. The memory properties of VFGOTM devices are comparable or even better than traditional planar FGOTM and much better than the reported organic nonvolatile memory with vertical transistor structures. More importantly, organic nonvolatile memory with vertical transistor structures is investigated for the first time on a flexible substrate. The results show that VFGOTM architecture allows vertical current flow across the channel layer to effectively eliminate the effect of mechanical bending during current transport, which significantly improves the mechanical stability of the flexible VFGOTM. Hence, with a combination of excellent driving ability, memory performance, and mechanical stability, VFGOTM devices meet the practical requirements for high performance memory applications, which have great potential for the application in a wide range of flexible and wearable electronics.     

Transparent Nanopaper‐Based Flexible Organic Thin‐Film Transistor Array

Eco‐friendly and low‐cost cellulose nanofiber paper (nanopaper) is a promising candidate as a novel substrate for flexible electron device applications. Here, a thin transparent nanopaper‐based high‐mobility organic thin‐film transistor (OTFT) array is demonstrated for the first time. Nanopaper made from only native wood cellulose nanofibers has excellent thermal stability (>180 °C) and chemical durability, and a low coefficient of thermal expansion (CTE: 5–10 ppm K^‐1). These features make it possible to build an OTFT array on nanopaper using a similar process to that for an array on conventional glass. A short‐channel bottom‐contact OTFT is successfully fabricated on the nanopaper by a lithographic and solution‐based process. Owing to the smoothness of the cast‐coated nanopaper surface, a solution processed organic semiconductor film on the nanopaper comprises large crystalline domains with a size of approximately 50–100 μm, and the corresponding TFT exhibits a high hole mobility of up to 1 cm²V^‐1 s^‐1 and a small hysteresis of below 0.1 V under ambient conditions. The nanopaper‐based OTFT also had excellent flexibility and can be formed into an arbitrary shape. These combined technologies of low‐cost and eco‐friendly paper substrates and solution‐based organic TFTs are promising for use in future flexible electronics application such as flexible displays and sensors.     

Fast Thin-Film Transistor Circuits Based on Amorphous Oxide Semiconductor

Five-stage ring oscillators (ROs) composed of amorphous In/Ga/Zn/O (a-IGZO) channel thin-film transistors (TFTs) with the channel lengths of 10 mum were fabricated on a glass substrate. The a-IGZO layer was deposited by RF magnetron sputtering onto the unheated substrate. The RO operated at 410 kHz (the propagation delay of 0.24 mus/stage), when supplied with an external voltage of +18 V. This is the fastest integrated circuit based on oxide-semiconductor channel TFTs to date that operates faster than the ROs using conventional hydrogenated amorphous silicon TFTs and organic TFTs     

A High-Performance Polysilicon Thin-Film Transistor Built on a Trenched Body

In this paper, a high-performance polysilicon thin-film transistor (poly-Si TFT) with a trenched body is proposed, fabricated, and studied. This new trenched TFT can be easily produced by filling and etch-back technology without destroying the channel film quality. The addition of the body trench is found to reduce the off-state leakage current by 70% on average, because the trench induces a carrier scattering effect in the poly-Si grain-boundary traps, thereby affecting the leakage path. Although the off-state current is substantially reduced, the on-state current is comparable with that of a conventional TFT. Our multiple-trenched-body TFT is also shown to improve the breakdown voltage by 11%.